A reception device for radio communication down-converts a high-frequency reception signal received by an antenna, by a mixer circuit (multiplier), so as to convert it into a reception signal of a lower frequency. The low-frequency reception signal is demodulated, and the transmitted data is output through decoding processing etc. The mixer circuit multiplies the high-frequency reception signal by a local signal generated by a local oscillator circuit. Among output signals of the mixer circuit, only low frequency components are extracted by a low-pass filter, so that high frequency components are eliminated. When the reception signal after the down-conversion is a baseband signal, the frequency of the local signal equals to the frequency of the reception signal. In the case that the reception signal after the down-conversion has an intermediate frequency, it is needed to set the local signal frequency to be equal to a difference between the reception signal frequency and the intermediate frequency.
Therefore, in order to receive a wide frequency range, it is needed to vary the local signal frequency in a wide range. However, it is not easy to make a signal generator circuit, which generates local signals, generate a wide frequency range of signals. For example, in the local signal generator circuit which includes a voltage controlled oscillator (VCO), it is not easy to broaden a variable width of the VCO, while the provision of a plurality of VCOs brings about an increased chip area.
Also, in a transmitter circuit for radio communication, a high-frequency circuit in its output stage has a mixer circuit to up-convert a modulated transmission signal into a communication frequency band. To this mixer circuit also, a local signal of the communication frequency band is supplied, similar to the above description, so that the modulated transmission signal is multiplied by the local signal. Therefore, it is also needed to supply a wide frequency range of different local signals to the mixer circuit of the transmission device.
Such local signal generator circuit are described in [Patent document 1] The official gazette of the Japanese Laid-open Patent Publication No. 2000-196418, [Patent document 2] The official gazette of the Japanese Laid-open Patent Publication No. 2009-105959, [Patent document 3] U.S. Pat. No. 6,404,293 B1, and [Non-patent document 1] H. Darabi, “A 2.4 GHz CMOS Transceiver for Bluetooth” IEEE J. Solid-State Circuits, vol. 36, pp. 2016-2024, December 2001